صدق الله العظيم الاسراء اية 58

By Dr. Abdel Aziz M. Hussein Lecturer of Physiology Member of American Society of Physiology

The retina is the innermost photosensitive layer of the eyeball. It contains about 55 types of cells and 70% of total sensory receptors Histologically, it is formed of 10 layers Physiologically, 4 layers have special importance

Pigmented Epithelium Photoreceptors Bipolar cells Ganglion cells

Contains large amounts of melanin pigments

Produces a sticky ECF matrix

continual renewal of the outer segment of the rods and cones.

Breakdown and Resynthesis of the Photopigments

Stores Large Amount of Vit. A

Rods and Cones

Outer Segment

Outer segment Inner segment Inner Segment

Rod 120 millions Rod 120 millions Cones 7 millions Cones 7 millions Rod One pigment (rhodopsin) Rod One pigment (rhodopsin) Cone 3 pigments (iodopsin) Cone 3 pigments (iodopsin) Rods and Cones

Rods are peripheral cones are central

Rods and Cones Convergence

Rod more sensitive to lightLess accurate Cannot perceive colours Night vision Cone less sensitive to lightmore accurateCan perceive coloursDay vision Rods and Cones Functions

Bipolar cells Ganglion cells 1 st order neuron 2 nd order neuron Rods and Cones Convergence

Central retinal artery Choroidal blood vessels Supply pigmented epithelium and photoreceptors Supply inner layer of retina

 Retinal detachment (occurs between the pigmented epithelium and photoreceptors)  In this case the retina can resist degeneration for days due to its own blood supply (from central retinal artery) and diffusion of fluids across the detachment gap.  If the retina is not replaced rapidly within few days degeneration of the retina occurs.

Fundus oculi is the part of the retina which can be seen by ophthalmoscope. Fovea centralis Optic disc

Fovea centralis

1. Decomposition of photosensitive pigment in rods & cones 2. Excitation of the photoreceptors by activated rhodopsin and generation of photoreceptor potential 3. Termination of excitation 4. Regeneration of photopigments

In DarkIn Dark

In LightIn Light

Within a sec the activated rhodopsin is inactivated by the enzyme rhodopsin kinase

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